1. Field of the Invention
The invention generally relates to the field of signal processing for wireless communications. More specifically the invention is relates to digital frequency-hopping transceivers and methods thereof.
2. Discussion of the Related Art
The IEEE 802.15.3a group is defining an international standard to enable reliable, cost-effective, high data rate communication for Wireless Personal Area Networks (WPANs) using UltraWide Bandwidth (UWB) signals. Multiband devices based on the Multi-Band OFDM Alliance (MBOA) proposal use 528-MHz-wide OFDM modulation to meet the 500-MHz minimum bandwidth requirements specified in US 47 CFR Part 15 Technical Requirements for Indoor UWB Systems. The multiband RF carrier is then frequency hopped within a specified band group to spread the signal over a much larger operating bandwidth. The MBOA proposal specifies a 3.1 to 10.6-GHz frequency range divided into 14 channels or bands. These bands are grouped into five Band Groups (1-5) consisting of four groups of three subbands each and one group of two subbands.
The current MB-OFDM specification uses an IFFT (Inverse Fast Fourier Transform) output sampling rate of 528 MHz. The OFDM signal consists of 128 sub-carriers. These carriers occupy a 528 MHz, so the sub-carrier spacing is 4.125 MHz. Since the carrier spacing is 4.125 MHz, it follows that the OFDM symbol length must be 1/4.125e6=242.42 ns. To allow for inter-symbol interference, a zero-energy prefix of 1/4 of the symbol length (60.6 ns) is applied in place of the more traditional cyclic prefix. Finally a guard period of 5 samples (9.47 ns) is added. The total OFDM symbol length is 312.5 ns.
The MB-OFDM specification uses a three-band hopping scheme to realize a three-fold increase in bandwidth. For example, successive OFDM symbols are transmitted in different bands according to a predefined hopping sequence of length 6. These hopping sequences are designed to minimize collisions between uncoordinated piconets and are known as Time-Frequency Interleaving (TFI) codes. Example sequences include {1,2,3,1,2,3}, {3,2,1,3,2,1}, {1,1,2,2,3,3} etc., where each index represents a specific 528 MHz frequency band.
In the prior art, a frequency-hopping controller is used to control the frequency of a carrier signal generated by a carrier frequency synthesizer. An information-bearing baseband signal can be modulated onto the carrier signal for transmission. In the baseband circuit of a conventional receiver, a packet detector is used to detect if a packet has been received. If the packet is detected, it will activate the frequency-hopping controller to sequentially output a frequency-hopping control signal to the carrier frequency synthesizer, and the carrier frequency synthesizer will then output the carrier signal. The received radio frequency (RF) signal will be down-converted and demodulated according to the carrier frequency to produce the original baseband signal.